Using colony-born stumptail monkeys (M. arctoides) we will study the development of the cerebral cortex and cerebellum during social rearing and sensory and motor deprivation rearing conditions. This study will extend previous work that concentrated on effects at 6 months of age to both earlier and later age levels. Understanding brain changes from birth to 2 years as functions of age and environment and relating these to behavioral changes are the overall objectives. Physical growth, behavioral changes, and changes in dendritic development in sensory and motor areas of the brain will be studied. Recovery or failure to recover in terms of these growth measures will be determined in animals that have been deprived for the initial 3 months after birth and then given social group rearing up to 6 months. Golgi-Cox and rapid Golgi techniques will be used for staining sections of cortical tissue. Drawings will be made of stellate cells and pyramidal cells from particular layers of specified areas. Our previous studies of layer IV stellate cells will be extended to both stellate and pyramidal cells of layers II and III, and V. Postnatal development of the cerebellum will be evaluated in terms of cell migration, growth of cell processes and cell soma in all three layers of the cerebellum.